Fosamprenavir Calcium is an antiviral compound, The chemical name of Fosamprenavir Calcium is Calcium (3S) tetrahydro-3-furanyl (1S,2R)-3-[[(4-aminophenyl)sulfonyl](isobutyl)amino]-1-benzyl-2-(phosphonooxy)propylcarbamate. Fosamprenavir Calcium has HIV aspartyl protease inhibitory activity and is particularly well suited for inhibiting HIV-1 and HIV-2 viruses. Moreover, Calcium (3S) tetrahydro-3-furanyl (1S,2R)-3-[[(4-aminophenyl)sulfonyl](isobutyl)amino]-1-benzyl-2-(phosphonooxy)propylcarbamate has increased solubility in the pH range of the gastro-intestinal tract compared to the HIV protease inhibitor [3S-[3R*(1R*,2S*)]]-[3-[[(4-aminophenyl)sulfonyl](2-methyl-propyl)amino]-2-hydroxy-1-phenylmethyl)propyl]-tetrahydro-3-furanyl ester (amprenavir, 141W94). Amprenavir, which has poor solubility and is thus available as a solution in gel capsules and has a high pill burden. This new HIV protease inhibitor with its increased solubility thus has the potential to reduce the perceived pill burden and may be formulated as a tablet.
The structure of Calcium (3S) tetrahydro-3-furanyl (1S,2R)-3-[[(4-aminophenyl)sulfonyl](isobutyl)amino]-1-benzyl-2-(phosphonooxy)propylcarbamate is shown below as Formula I

U.S. Pat. No. 6,436,989B1 patent disclosed Fosamprenavir and its pharmaceutically acceptable salts, A wide range of salts of Fosamprenavir were made in this patent viz. di-sodium, di-potassium, magnesium, zinc, ethylene diamine, piperazine etc. Of these, the piperazine salt was a crystalline solid, but had the practical disadvantage of toxicity at the anticipated dose.
U.S. Pat. No. 6,514,953B1 patent disclosed crystalline form 1 of calcium salt of (3S)-tetrahydrofuran-3-yl(1S,2R)-3-[[(4-aminophenyl)sulfonyl](isobutyl)amino]-1-benzyl-2-(phosphonooxy) propylcarbamate.
WO2010134045 publication disclosed an amorphous Fosamprenavir Calcium and process for the preparation of amorphous Fosamprenavir Calcium.
WO 2011001383 publication disclosed crystalline form II of Fosamprenavir Calcium and a process for the preparation of crystalline form II of Fosamprenavir Calcium.
WO2011085130 publication disclosed rod like amorphous, form II, form III; form IV and form P.